When a freehand medical intervention treatment is carried out, an ultrasound image is commonly used to monitor the intervention, so as to reduce injuries to organs and tissues on a needle path as much as possible. For example, when conducting a freehand thyroid nodule biopsy, or carrying out a removal therapy, such as radiofrequency ablation (RFA), on a thyroid nodule or a liver tumor using a needle electrode, the ultrasound image is obtained to indicate the positions of tissues inside the body, so that the user may refer to the ultrasound image and control a needle body accordingly to perform an operation on a target while avoid injuries to nerves or other organs and tissues.
However, before the needle is inserted into the body that is under the field of view of the ultrasound transducer, the ultrasound image is unable to indicate relative positions between the needle body and the tissues inside the body. Hence, it is challenging for the user to determine the preferable position and angle to insert the needle into the body based on the ultrasound image.